Elemental sulfur is widely used in the agricultural and chemical industries as a soil amendment, with or without other components, as a chemical precursor (sulfuric acid) and as a compound in elastomeric, paint, road surface and structural material formulations.
The present invention involves the improvement of several sulfur properties, particularly those properties that influence agronomic use, compounding or formulation with hydrophobic materials, and general ease and safety of transport and handling. Relevant properties include grindability, particle fluidity, bridging in process or transport equipment, water retention, and resistance to oxidation and corrosion.
These compositions comprise homogeneous distributions of certain hydrocarbons in an elemental sulfur matrix. They may or may not contain other components as desired. The oil is distributed evenly throughout a continuous sulfur matrix. This property provides a predetermined hydrocarbon-sulfur ratio regardless of grinding, or particle consumption in use. It allows for higher hydrocarbon loadings and reduced surface cohesiveness at high loading and reduces agglomeration and bridging.
In these and other respects these compositions are superior to other hydrocarbon-sulfur combinations suggested in the prior art. For instance, Block U.S. Pat. No. 3,661,530 suggests that several deficiencies of dusting sulfur can be minimized by post manufacture sulfur application of a variety of hydrocarbon compounds. Block was concerned primarily with fluidity (sulfurs that remain free-flowing) and agglomeration or anti-caking qualities which are known problems with finely divided sulfurs.
Undoubtedly Block's procedures reduce the magnitude of these problems. However, I have found that surface application has several disadvantages. Only a limited amount of hydrocarbon can be retained on the particle surface, and even less than this limit should be added to avoid agglomeration (depending on hydrocarbon properties and conditions of use). Excess hydrocarbon which is tacky during use will itself cause agglomeration and the problems which Block seeks to avoid. More importantly, the continuous sulfur-hydrocarbon interface will persist only so long as the particles are not further comminuted, degraded or consumed during use by bacterial action, grinding, or high shear blending. Any of these common occurrences will expose uncoated surfaces.
In contrast, the compositions of this invention do not suffer the same deficiencies. Particles obtained by fracturing larger particles or blocks still contain hydrocarbon disposed throughout the sulfur matrix since, in the first instance, the hydrocarbon is not simply coated on the exterior surface of the block, particle, etc., or contained in some coating that covers only the particle or block surface. Thus, no matter how small the blocks or particles are ground by any procedure, the resulting particles and dust contain the amount of hydrocarbon desired.
It is therefore one object of this invention to provide improved hydrocarbon-sulfur combinations. Another object is the provision of a homogeneous sulfur-hydrogen blend in which the hydrocarbon is evenly distributed throughout a continuous sulfur matrix. Another object is the provision of sulfur particles which are less hygroscopic, are more fluid, and therefore have less tendency to bridge or plug equipment, are less corrosive, and have less tendency to dust. Another object is the provision of hydrocarbon-containing sulfur particles of hydrocarbon loading and acceptably low surface tack.
Yet another object is the provision of hydrocarbon-containing sulfurs which are particularly suitable soil amendments due to the relatively constant ratio of hydrocarbon and sulfur throughout the particle matrix. Soil sulfurs are gradually converted to sulfates by sulfur-active bacteria (thiobacilli). Some of these bacteria are homotropic (autotropic) in that they require sulfur as their only solid nutrient. However, many more species are heterotropic, and they also require a non-toxic carbon source.
Obviously heterotropic thiobacilli can initially obtain both sulfur and hydrocarbon from hydrocarbon-coated sulfurs such as those described in U.S. Pat. No. 3,661,530. However, the oil coating gradually dissipates due to bacterial action and/or ground water leaching. The partially consumed or leached particles then present an environment--carbon-free, pure sulfur--that will not support heterotropic species.
That is not the case with the compositions of this invention. They are homogeneous; the hydrocarbon is evenly distributed throughout the sulfur matrix.
Similar problems would arise with sulfurs originally provided in blocks or large particles and later ground into smaller sizes. The major surface of the fractured particles contains no hydrocarbon. These surfaces would not present the best environment for bacterial activity--sulfur conversion to sulfate.
I have found that fracturing hydrocarbon-coated sulfurs also reduces product quality in other respects. The uncoated surfaces become hygroscopic (once oxidized) which detracts from overall water repellancy. Such products are more corrosive, less fluid, and have more tendency to dust.
I have also found that the presence of hydrocarbon at the particle surface significantly reduces bridging and plugging during transport and use. However, this property is lost, at least in degree, in heterogeneous particles which are fractured after coating.
The inadequacies of prior art compositions can be overcome, at least in degree, by producing particles which comprise the homogeneous combination of a continuous sulfur matrix and certain hydrocarbons evenly distributed throughout that matrix. I have discovered that these hydrocarbons can be compounded into homogeneous molten sulfur blends, and that they remain evenly dispersed in both the melt and solid phases during quenching, particle formation, storage and use.
My procedure also avoids the need for surfactants which, as suggested by Block, supra, are required to obtain adequate hydrocarbon coverage of hydrophilic (oxidized) sulfur surfaces. In fact, I have found that it is often preferable to exclude surfactants due to their reactivity with the sulfur melt and potential toxicity in agronomic use.
While the hydrocarbon does not intolerably weaken the particle product, even at relatively high hydrocarbon loadings, the products are somewhat more friable than are hydrocarbon-free materials. Thus, they are sufficiently hard to retain their size and shape during conventional handling yet require less energy for grinding, if desired.
These methods and compositions also allow higher hydrocarbon loadings than does surface application. They assume a constant oil-to-sulfur ratio throughout each particle. Thus a predetermined ratio can be maintained even after grinding or during use. This homogeneity also assures the continuity of certain physical properties even in ground or partially consumed products. Thus at all stages the particles are free-flowing, hydrophobic, and non-corrosive.
Regardless of fracturing or crushing after manufacture, these products have less tendency to dust and maintain their improved affinity for non-polar, hydrophobic substances. This property is desirable for compounding with non-polar materials such as rubber, oil-based paints and similar compositions. Such compositions are more stable and are easier to produce in the first instance.
In accordance with one embodiment, these methods involve forming a melt containing at least 60 weight percent elemental sulfur at a melt temperature of about 120.degree. to about 400.degree. C. and homogeneously dispersing throughout the melt at least about 0.2 weight percent of the hydrocarbon and solidifying the resulting blend. The combinations can be subdivided during or after quenching it desired. They are homogeneous and comprise a continuous rhombic sulfur matrix with the hydrocarbon evenly distributed throughout.
The compositions of this invention can contain essentially any type of hydrocarbon including hydrocarbons that may react to a slight extent with sulfur at the melt temperature or otherwise. For obvious reasons, however, I generally prefer to minimize the amount of reactive hydrocarbons in the mixture to avoid unnecessary process complications and the introduction of possibly unnecessary toxic materials. Thus reactive hydrocarbons such as olefins, alkynes, etc., should be kept to a minimum in most circumstances, e.g., at a level of less than about 15 percent, preferably less than 1 percent of total hydrocarbon.
In the case of formulations intended for agricultural use, the hydrocarbon is preferably selected from non-toxic materials that are not reactive with sulfur under reaction conditions. These include principally the paraffinic and alkyl substituted and unsubstituted aromatic hydrocarbons and combinations of these. The hydrocarbon boiling and melting points are determined primarily in view of the conditions required to obtain the compositions of this invention. Since the presently preferred method involves addition of the hydrocarbon to the sulfur melt, distribution of the hydrocarbon throughout the melt, and cooling to form the homogeneous fusions, the hydrocarbon should have a boiling point above the selected melt temperature and a melting point below the selected temperature. This criteria allows for considerable variation as will be understood by practitioners skilled in this art. The preferred manufacturing methods contemplate melt temperatures of about 120.degree. to about 400.degree. C. Thus, as a general rule, the hydrocarbon will have melting points below 400.degree. C. and boiling points above 120.degree. C. Obviously, higher boiling hydrocarbons should be used at higher melt temperatures. Similarly, higher melt temperatures should be used with higher melting point hydrocarbons that might not melt and/or distribute adequately at lower melt temperatures. Thus the practitioner can easily select the melt temperature and hydrocarbon melting and boiling points that best accommodate his situation.
Suitable hydrocarbons include virgin or partially refined crudes or synthetic crudes derived from coal, oil shale or other origins of natural or synthetic paraffins, aromatics and/or alkyl aromatics and combinations thereof. Illustrative are paraffin waxes, gas oils, crude oil, reduced crude oil residuum, naphtha, diesel oil, fuel oil, light and heavy gas oils, kerosene, jet fuel, 80 to 300 neutral oils, paraffin waxes, hydrocarbon homo- or heteropolymer oils, waxes or thermoplastics such as polyolefins, polystyrene, and the like.
The hydrocarbons preferred for agricultural use should be non-polar and non-reactive with sulfur or other components of the composition at melt temperature. They are preferably paraffinic, aromatic, or alkyl aromatic or combinations of these. They should be liquid at the melt temperature and thus should have a melting point below and a boiling point above melt temperature. Usually the hydrocarbon will melt at least about 10.degree. C. and preferably about 20.degree. C. below melt temperature and will have a boiling point of at least 10.degree. C., preferably at least about 20.degree. C. above melt temperature. However, I have found they need not be solid at ambient conditions since the great majority of the hydrocarbon is confined in the sulfur matrix. In some applications, higher melting hydrocarbons, e.g., those having melting points above ambient, may be preferred at the higher loadings, e.g., above 15 weight percent, to reduce surface tack.
Due to the preference for non-reactive, non-toxic hydrocarbons in compositions intended for agricultural use, the hydrocarbon should be substantially free of olefins, alkynes, alkenyl aromatics and, in those products, should not contain reactive functional groups such as hydroxyl, amino, ether, aldo, keto, or carboxyl groups, or the like. This exclusion does not include most halogenated hydrocarbons which are generally unreactive, at least at the lower temperature. Aromatics are somewhat refractive to bacteria. Accordingly, paraffins are particularly preferred for agronomic use.
Hydrocarbon loadings are usually at least 0.2 weight percent up to about 40 weight percent, normally 0.2 to about 20, and preferably 0.2 to about 10 weight percent based on total weight. Most uses involve loadings of 0.2 to about 5 percent.
While the desirable properties are generally reflected in particles of any size, most applications will require, or are at least better served by particles having average diameters of less than about 1 inch, usually less than about 3/4 inch. Numerous methods of obtaining such particles are well known in the art. Surprisingly, such particles can be obtained without excessive hydrocarbon loss even in high shear contacting with aqueous quench media.
These compositions can contain other components which are thermally stable and non-reactive with the hydrocarbon or sulfur melt. Illustrative are fertilizers including major and micronutrients, fillers such as clays, pigments, and essentially any solid or molten, thermally stable, unreactive substance.
Melt temperatures range from about 120.degree. to about 400.degree. C. Problems of reactivity and thermal stability are less severe at the lower temperatures. The hydrocarbon is blended with the sulfur melt with sufficient agitation to assure homogeneity. The blend is then quenched into blocks or particles as desired.
These methods do not require surfactants for adequate hydrocarbon distribution. In fact, such materials are preferably avoided, at least in most applications, due to their reactivity at melt temperatures or their toxicity or relative refractiveness toward heterotropic sulfur-active bacteria. Moreover, surfactants would be largely wasted in the preferred particle forming techniques which involve quenching and subdividing the melt in an aqueous phase. At least some of the surfactant would be abstracted from the sulfur particles, at least from the surface. Surfactant removal results in hydrocarbon leaching from the sulfur matrix.
The melt can be quenched and, if desired, can be comminuted by essentially any known procedure. Such methods do not constitute an essential aspect of this invention. However, I have found that the blends are suitable for water quenching since very little hydrocarbon is lost, at least in the absence of surfactants. Thus the melt can be cooled into blocks and crushed to the desired particle size or it can be air cooled by conventional methods such as prilling towers.
Particularly preferred methods involve water quenching by any one of several techniques. The melt can be sprayed into a standing or agitated aqueous quench in which case particle size can be regulated by spray size and, to some extend, by agitation. Other methods involve pouring a melt into an agitated aqueous quench, in which case particle size is determined primarily by agitation severity.
A particularly preferred method is disclosed in my U.S. Pat. Nos. 3,637,351, 3,769,378 and 3,830,361, which are incorporated herein by reference. Briefly, these methods involve contacting a high velocity water spray with a high velocity spray of the homogeneous sulfur-hydrocarbon melt to form a highly turbulent zone of intersection of the two sprays in which the homogeneous composition is simultaneously subdivided and quenched into the porous particles similar to those described in the noted patents.